Transmitter optical subassembly (TOSA) with laser diode driver (LDD) circuitry mounted to feedthrough of TOSA housing

ABSTRACT

The present disclosure is generally directed to a multi-channel TOSA arrangement with a housing that utilizes a feedthrough device with at least one integrated mounting surface to reduce the overall dimensions of the housing. The housing includes a plurality of sidewalls that define a hermetically-sealed cavity therebetween. The feedthrough device includes a first end disposed in the hermetically-sealed cavity of the housing and a second end extending from the cavity away from the housing. The feedthrough device provides the at least one integrated mounting surface proximate the first end within the hermetically-sealed cavity. At least a first laser diode driver (LDD) chip mounts to the at least one integrated mounting surface of the feedthrough device. A plurality of laser arrangements are also disposed in the hermetically-sealed cavity proximate the first LDD chip and mount to, for instance, a LD submount supported by a thermoelectric cooler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of co-pending U.S. patentapplication Ser. No. 16/295,586 filed on Mar. 7, 2019, which is fullyincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to optical communications and moreparticularly, to a transmitter optical subassembly (TOSA) having a laserdiode driver (LDD) and associated circuitry mounted to a feedthrough ofa housing of the TOSA.

BACKGROUND INFORMATION

Optical transceivers are used to transmit and receive optical signalsfor various applications including, without limitation, internet datacenter, cable TV broadband, and fiber to the home (FTTH) applications.Optical transceivers provide higher speeds and bandwidth over longerdistances, for example, as compared to transmission over copper cables.The desire to provide higher transmit/receive speeds in increasinglyspace-constrained optical transceiver modules has presented challenges,for example, with respect to thermal management, insertion loss, RFdriving signal quality and manufacturing yield.

Optical transceiver modules generally include one or more transmitteroptical subassemblies (TOSAs) for transmitting optical signals. TOSAscan include one or more lasers to emit one or more channel wavelengthsand associated circuitry for driving the lasers. Some opticalapplications, such as long-distance communication, can require TOSAs toinclude hermetically-sealed housings with arrayed waveguide gratings,temperature control devices, laser packages and associated circuitrydisposed therein to reduce loss and ensure optical performance. However,the inclusion of hermetically-sealed components increases manufacturingcomplexity, cost, and raises numerous non-trivial challenges withinspace-constrained housings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood byreading the following detailed description, taken together with thedrawings wherein:

FIG. 1 is a block diagram of a multi-channel optical transceiver,consistent with embodiments of the present disclosure.

FIG. 2 is a perspective view of a multi-channel optical transceivermodule consistent with the present disclosure.

FIG. 3 is a side view of the multi-channel optical transceiver module ofFIG. 2, consistent with an embodiment of the present disclosure.

FIG. 4A shows a top-down view of a multi-channel TOSA arrangement of themulti-channel optical transceiver module of FIG. 2, in accordance withan embodiment of the present disclosure.

FIG. 4B shows an enlarged portion of the multi-channel TOSA arrangementof FIG. 4A.

FIG. 5 shows another perspective view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 6 shows another perspective view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 7 shows a cross-sectional view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 8A shows another cross-sectional view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 8B shows an enlarged view of the feedthrough device of FIG. 8A inaccordance with an embodiment.

FIG. 9A shows another cross-sectional view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 9B shows an enlarged view of the feedthrough device of FIG. 9A inaccordance with an embodiment.

FIG. 10A shows another cross-sectional view of the multi-channel TOSAarrangement of FIG. 4A in accordance with an embodiment of the presentdisclosure.

FIG. 10B shows an enlarged view of the feedthrough device of FIG. 10A inaccordance with an embodiment.

DETAILED DESCRIPTION

As discussed above, significant challenges limit increased channelconfigurations of optical transceiver modules beyond four (4) channelsto achieve transmission speeds in excess of 100 gb/s. One such challengeincludes designing transmitter optical subassembly (TOSA) housings withfootprints as small as possible while also providing sufficient space toallow for mounting of components and distances between opticalcomponents that facilitates thermal dissipation, reduce electricalinterference, and maintains radio frequency (RF) driving signalintegrity, for example.

In the context of multi-channel TOSAs with channel counts in excess offour (4), these challenges can be further exacerbated by the duplicationof some optical components to achieve a desired channel count. Forinstance, LDD chips are often limited to driving four or less channels,thus necessitating redundantly including two LDD chips and supportingcircuitry to facilitate, for instance, eight (8) total channels. Theseconsiderations and challenges are of significant import in TOSA designsthat utilize hermetically-sealed housings as a substantial portion ofthe overall cost to manufacture each TOSA is directly related to thedimensions/volume of the hermetically-sealed cavity. Continued scalingof hermetically-sealed TOSA housings thus depends in part on TOSAcircuitry configurations (both inside and outside of the TOSA housing)that achieve nominal power, RF signal quality, and thermal dissipationrequirements, while also minimizing the volume of thehermetically-sealed cavity.

Thus, the present disclosure is generally directed to a multi-channelTOSA arrangement with a housing that utilizes a feedthrough device withat least one integrated mounting surface. In more detail, the housingincludes a plurality of sidewalls that define a hermetically-sealedcavity therebetween. The feedthrough device includes a first enddisposed in the hermetically-sealed cavity of the housing and a secondend extending from the cavity away from the housing. The feedthroughdevice provides the at least one integrated mounting surface, which maybe referred to herein as simply a mounting surface, proximate the firstend within the hermetically-sealed cavity. At least a first laser diodedriver (LDD) chip mounts to the at least one integrated mounting surfaceof the feedthrough device. A plurality of laser arrangements are alsodisposed in the hermetically-sealed cavity proximate the first LDD chipand mount to, for instance, a LD submount supported by a thermoelectriccooler (TEC). Each of the laser arrangements of the plurality of laserarrangements electrically couples to the first LDD chip via, forexample, wire bonds.

In an embodiment, the at least one integrated mounting surface of thefeedthrough device includes a multi-step profile whereby first andsecond mounting surfaces extend substantially parallel to each other andsubstantially transverse relative to a surface that adjoins the two. Inthis embodiment, at least a first LDD chip mounts to the first or thesecond mounting surface and at least one filtering capacitor couples tothe other of the first or the second mounting surface. Accordingly, themulti-step profile permits LDD chips and filtering capacitors tophysically and electrically mount to the feedthrough devices ondifferent steps/tiers. The LDD chips and filtering capacitors thenelectrically couple to the plurality of laser arrangements by way of,for example, wire bonds.

Numerous advantageous will be apparent in light of the presentdisclosure relative to other TOSA design approaches. For example, the atleast one integrated mounting surface of the feedthrough device allowsfor one or more LDD chips to be mounted thereon within thehermetically-sealed housing rather than on a printed circuit board (PCB)or other location within the TOSA housing. Accordingly, the space whichLDD chips normally occupy within the hermetically-sealed housing becomesavailable for other optical components to be mounted such as theplurality of laser arrangements. This advantageously permits theplurality of laser arrangements to be disposed proximate the feedthroughdevice, e.g., without LDD chips therebetween, while also maintaining arelatively short distance to the LLD chips. The TOSA housing, and byextension the hermetically-sealed cavity, may then be reduced in overalllength as the substrate/submount supporting the TOSA optical componentscan be shortened as a result of the feedthrough device providingmounting surfaces for the LDD chip and/or filtering capacitors.Likewise, the feedthrough device can provide mounting space forfiltering capacitors that significantly improve TOSA performance. Thus,a multi-channel TOSA consistent with the present disclosure allows forinclusion of filtering capacitors that are often omitted intentionallyfor space-saving purposes.

The feedthrough device with the one more integrated mounting surfacesfurther advantageously provides thermal isolation between the laserarrangements and the LDD chips. For example, the feedthrough device canprovide a thermal conduction path separate and isolated from a thermalconduction path of the plurality of laser arrangements. The thermalconduction path of the feedthrough device also allows for greaterdissipation by virtue of the material forming the device, e.g., ceramic.Accordingly, less power may be consumed by a multi-channel TOSAconsistent with the present disclosure during operation based on the TECbeing utilized to cool the plurality of laser arrangements rather thanboth the plurality of laser arrangements and LDD chips.

As used herein, “channel wavelengths” refer to the wavelengthsassociated with optical channels and may include a specified wavelengthband around a center wavelength. In one example, the channel wavelengthsmay be defined by an International Telecommunication (ITU) standard suchas the ITU-T dense wavelength division multiplexing (DWDM) grid. Thisdisclosure is equally applicable to coarse wavelength divisionmultiplexing (CWDM). In one specific example embodiment, the channelwavelengths are implemented in accordance with local area network (LAN)wavelength division multiplexing (WDM), which may also be referred to asLWDM.

The term “coupled” as used herein refers to any connection, coupling,link or the like and “optically coupled” refers to coupling such thatlight from one element is imparted to another element. Such “coupled”devices are not necessarily directly connected to one another and may beseparated by intermediate components or devices that may manipulate ormodify such signals. On the other hand, the term “direct opticalcoupling” refers to an optical coupling via an optical path between twoelements that does not include such intermediate components or devices,e.g., a mirror, waveguide, and so on, or bends/turns along the opticalpath between two elements.

The term substantially, as generally referred to herein, refers to adegree of precision within acceptable tolerance that accounts for andreflects minor real-world variation due to material composition,material defects, and/or limitations/peculiarities in manufacturingprocesses. Such variation may therefore be said to achieve largely, butnot necessarily wholly, the stated/nominal characteristic. To provideone non-limiting numerical example to quantify “substantially,” such amodifier is intended to include minor variation that can cause adeviation of up to and including ±5% from a particular statedquality/characteristic unless otherwise provided by the presentdisclosure.

As used herein, the terms hermetic-sealed and hermetically-sealed may beused interchangeably and refer to a housing that releases a maximum ofabout 5*10⁻⁸ cc/sec of filler gas. The filler gas may comprise an inertgas such as nitrogen, helium, argon, krypton, xenon, or various mixturesthereof, including a nitrogen-helium mix, a neon-helium mix, akrypton-helium mix, or a xenon-helium mix.

Referring to the Figures, FIG. 1, an optical transceiver 100, consistentwith embodiments of the present disclosure, is shown and described. Theoptical transceiver module 100 is shown in a highly simplified form forclarity and ease of explanation and not for purposes of limitation. Inthis embodiment, the optical transceiver 100 includes a multi-channeltransmitter optical subassembly (TOSA) arrangement 104 and amulti-channel receiver optical subassembly (ROSA) arrangement 106coupled to a substrate 102, which may also be referred to as an opticalmodule substrate. The substrate 102 may comprise, for example, a printedcircuit board (PCB) or PCB assembly (PCBA). The substrate 102 may beconfigured to be “pluggable” for insertion into an optical transceivercage 111.

In the embodiment shown, the optical transceiver 100 transmits andreceives eight (8) channels using eight different channel wavelengths(λ1 . . . λ8) via the multi-channel TOSA arrangement 104 and themulti-channel ROSA arrangement 106, respectively, and may be capable oftransmission rates of at least about 25 Gbps per channel, and preferably50 Gbps per channel. The optical transceiver 100 may also be capable oftransmission distances of 2 km to at least about 10 km. The opticaltransceiver 100 may be used, for example, in internet data centerapplications or fiber to the home (FTTH) applications. Although thefollowing examples and embodiments show and describe a 8-channel opticaltransceiver, this disclosure is not limited in this regard. For example,the present disclosure is equally applicable to 2, 4, 6-channelconfigurations.

In more detail, the multi-channel TOSA arrangement 104 includes a TOSAhousing 109 with a plurality of sidewalls that define a cavity. Thecavity includes a plurality of laser arrangements 110, a multiplexingdevice 125, and a feedthrough device 116 disposed therein. Themulti-channel TOSA arrangement 104 may be implemented as themulti-channel TOSA arrangement 204 of FIGS. 2-7 with at least one laserdiode driver (LDD) disposed/mounted on the feedthrough device 116, whichwill be discussed in greater detail below. In an any event, each laserarrangement of the plurality of laser arrangements 110 can be configuredto transmit optical signals having different associated channelwavelengths. Each laser arrangement can include passive and/or activeoptical components such as a laser diode (LD), optical isolator, focuslens, monitor photodiode (MPD), and so on.

To drive the plurality of laser arrangements 110, the opticaltransceiver 100 includes a transmit connecting circuit 112 to provideelectrical connections to the plurality of laser arrangements 110 withinthe housing 109. The transmit connecting circuit 112 may be configuredto receive driving signals (e.g., TX_D1 to TX_D8) from, for example,circuitry within the optical transceiver cage 111. The housing 109 maybe hermetically sealed to prevent ingress of foreign material, e.g.,dust and debris. Therefore, a plurality of transit (TX) traces 117 (orelectrically conductive paths) may be patterned on at least one surfaceof the substrate 102 and electrically coupled to a feedthrough device116 of the TOSA housing 109 to bring the transmit connecting circuit 112into electrical communication with the plurality of laser arrangements110, and thus, electrically interconnect the transmit connecting circuit112 with the multi-channel TOSA arrangement 104. The feedthrough device116 may comprise, for instance, ceramic, metal, or any other suitablematerial.

In operation, the multi-channel TOSA arrangement 104 may then receivedriving signals (e.g., TX_D1 to TX_D8), and in response thereto,generate and launch multiplexed channel wavelengths on to an outputwaveguide 120 such as a transmit optical fiber. The generatedmultiplexed channel wavelengths may be combined based on a multiplexingdevice 125 such as an arrayed waveguide grating (AWG) that is configuredto receive emitted channel wavelengths 126 from the plurality of laserarrangements 110 and output a signal carrying the multiplexed channelwavelengths on to the output waveguide 120 by way of optical fiberreceptacle 122.

Continuing on, the multi-channel ROSA arrangement 106 includes ademultiplexing device 124, e.g., an arrayed waveguide grating (AWG), aphotodiode (PD) array 128, and amplification circuitry 130, e.g., atransimpedance amplifier (TIA). An input port of the demultiplexingdevice 124 may be optically coupled with a receive waveguide 134, e.g.,an optical fiber, by way of an optical fiber receptacle 136. An outputport of the demultiplexing device 124 may be configured to outputseparated channel wavelengths on to the PD array 128. The PD array 128may then output proportional electrical signals to a TIA (e.g., TIAs130-1, 130-2), which then may be amplified and otherwise conditioned.The PD array 128 and the transimpedance amplifier 130 detect and convertoptical signals into electrical data signals (RX_D1 to RX_D8) that areoutput via the receive connecting circuit 132. In operation, the PDarray 128 may then output electrical signals carrying a representationof the received channel wavelengths to a receive connecting circuit 132by way of conductive traces 119 (which may be referred to as conductivepaths).

Referring to FIGS. 2-7 an example transceiver module 200 is shownconsistent with an embodiment of the present disclosure. The exampletransceiver module 200 may be implemented as the optical transceiver 100of FIG. 1. As shown, the optical transceiver module 200 includes aconfiguration to send and receive eight (8) different channelwavelengths in order to provide transmission speeds up to and an inexcess of 400 Gb/s, for instance. However, other channel configurationsare within the scope of this disclosure and the embodiment of FIGS. 2-7are not intended to limit the present disclosure.

In more detail, the optical transceiver module 200 includes a substrate202, multi-channel TOSA arrangement 204, and a multi-channel ROSAarrangement 206. In particular, the substrate 202 includes a first end203 that extends to a second end 205 along a longitudinal axis 250. Afirst and second mounting surface 245, 246 disposed facing away fromeach other extend in parallel along the longitudinal axis 250 and defineat least a portion of the substrate 202. The substrate 202 may comprise,for example, a printed circuit board assembly (PCBA) or other suitablesubstrate material. The multi-channel ROSA arrangement 206 is coupled toand supported by the first mounting surface 245 at a position proximatethe first end 203 of the substrate 202. The multi-channel ROSAarrangement 206 can include on-board/integrated configuration asdiscussed and described in greater detail in the co-pending U.S. patentapplication Ser. No. 16/142,466 filed on Sep. 28, 2018 and entitled“Receiver Optical Subassembly (ROSA) Integrated On Printed Circuit BoardAssembly,” the entirety of which is incorporated herein by reference.

As shown in FIG. 2, the multi-channel ROSA arrangement 206 includes ademultiplexing device 224, e.g., an arrayed waveguide grating (AWG),with an input port 229 coupled to an optical coupling receptacle 236 byway of an intermediate waveguide 211 (e.g., an optical fiber). Thedemultiplexing device 224 further includes an output region aligned witha photodiode (PD) array 228. The PD array 228 electrically couples tothe first and second amplification chips 230-1, 230-2, e.g.,transimpedance amplifiers (TIAs). In operation, a multiplexed opticalsignal received via the optical coupling receptacle 236 getsdemultiplexed by the demultiplexer 224. The demultiplexer 224 thenoutputs separated channel wavelengths on to corresponding photodiodes ofthe PD array 228. In turn, the PD array 228 outputs an electricalcurrent to the amplification circuitry 230-1, 230-2 that isrepresentative of the received and separated channel wavelengths. Theamplification circuitry 230-1, 230-2 then amplifies the electricalcurrents from the PD array 228 and outputs a signal to, for instance, adata bus via the receive connecting circuit 132 (FIG. 1).

The multi-channel TOSA arrangement 204 is coupled to the first end 203of the substrate 202 and includes a plurality of laser arrangements andoptical connectors for outputting a plurality of channel wavelengths, asdiscussed in greater detail below. The TOSA arrangement 204 may be edgemounted to the substrate 202, as shown, although other suitableapproaches are within the scope of this disclosure.

Turning specifically to the embodiment shown in FIG. 4A, the TOSAarrangement 204 includes a housing 209, which may also be referred to asa TOSA housing. The housing 209 is defined by a plurality of sidewalls256-1 to 256-6 that define a cavity 260 therebetween. Note, theembodiment shown in FIG. 4A omits the top cover of the TOSA housingmerely for clarity. The plurality of sidewalls 256-1 to 256-6 extendfrom a first end 261 to a second end 263 along the longitudinal axis 250(FIG. 2). However, the housing 209 may have other shapes andconfigurations and the provided example is not intended to be limiting.

As further shown in the embodiment of FIG. 4A, with additional referenceto FIG. 6, the TOSA arrangement 204 includes a feedthrough device 270, aplurality of laser arrangements 274, a multiplexing device 225, anoptical isolator chip 276 and an output port 279. The feedthrough device270 is disposed proximate the first end 261 of the housing 209 andextends at least partially into the cavity 260. In particular, a firstportion 232-1 of the feedthrough device 270 extends at least partiallyinto the cavity 260 and a second portion 232-2 may extend from thecavity 260 towards the substrate 202 for coupling purposes (see FIG. 6).Accordingly, the feedthrough device 270 defines at least a portion ofthe cavity 260.

The feedthrough device 270 may comprise, for example, a suitably rigidnon-metal material such as inorganic material such as a crystallineoxide, nitride or carbide material, which may be commonly referred to asceramic. Some elements, such as carbon or silicon, may also beconsidered ceramics, and are also within the scope of this disclosure.

Following the feedthrough device 270 a plurality of laser arrangements274 are at least partially disposed on laser diode (LD) submounts 280-1,280-2. Each laser arrangement of the plurality of laser arrangements 274includes a laser diode, a monitor photodiode, and a focus lens. Eachlaser arrangement also includes a corresponding LD driver (LDD) chip(e.g., LDD chip 242-1) mounted to the feedthrough device 270. Forexample, as shown in the enlarged region of FIG. 4B, each of the laserarrangements 274 can include a laser diode that is disposed at asubstantially uniform distance of D1 from an associated LDD chip, e.g.,LDD chip 242-1. The embodiment of FIG. 4B also shows that each of theplurality of laser diodes 274 and associated LDD chip, e.g., LDD chip242-1, may be mounted in a manner that causes the same to extenddirectly up to the edge of their respective mounting surfaces. To thisend, only a relatively small air gap 285 (also having an overall widthof D1) separates each of the laser diodes 274 and the associated LDDchips 242. As discussed in greater detail, the proximity of each LD chipto an associated LDD chip can significantly shorten the length of aninterconnect device between the same, such as a wire bond. In addition,the gap 285 can advantageously provide thermal isolation.

Following the plurality of laser arrangements 274, a multiplexing device225 is disposed at a midpoint within the cavity 260. In particular, themultiplexing device 225 includes an input region 282 facing the firstend 261 of the housing 209, and more particularly the plurality of laserarrangements 274. The input region 282 includes a plurality of inputports (not shown) that are aligned to receive channel wavelengths fromLDs along an associated light path. Each of the laser arrangements 274may then emit associated channel wavelengths on a corresponding lightpath of a plurality of input light paths 286 that intersect with theinput region 282, which is more clearly shown in FIG. 5. Each light pathof the plurality of light paths 286 therefore extends from an emissionsurface of an associated LD through a focus lens, and then ultimately tothe input region 282.

The multiplexing device 225 further includes an output port 284 that isdisposed opposite the input region 282 such that the output port 284faces the second end of the housing 209. The output port 284 outputs amultiplexed signal along an output light path 290. An optical isolator276 proximate the second end 263 of the housing 209 includes an aperture277, by which the output light path 290 extends therethrough. Followingthe optical isolator 276, the housing 209 includes an opening/aperturefor coupling to an optical coupling receptacle 292. The optical couplingreceptacle 292 optically couples with the transmit optical couplingreceptacle 222 by way of an intermediate fiber 294. Accordingly, themultiplexing device 225 outputs a multiplexed optical signal fortransmission via light path 290.

Turning to FIG. 6, additional aspects of a feedthrough device 270consistent with the present disclosure are shown. As shown, feedthroughdevice 270 may be defined by at least a first mounting surface 272-1 anda second mounting surface 272-2. Although denoted as “first” and“second,” these designations are merely for purposes of clarity and areutilized simply to distinguish between the mounting surfaces 272-1,272-2. To this end, either mounting surface may be referred to as a“first” or “second” surface. In any event, the first and second mountingsurfaces 272-1, 272-2 may be formed integrally with the feedthroughdevice 270 as a single piece, e.g., allowing for direct coupling ofcomponents to the feedthrough device 270. However, in some cases thefirst and second mounting surfaces 272-1, 272-2 may be provided by oneor more submounts. In either case, the feedthrough device 270advantageously provides mounting regions that facilitate such direct orindirect mounting and support of components.

Continuing on, the first and second mounting surfaces 272-1, 272-2 maybe substantially planar, such as shown, although the first and secondmounting surfaces 272-1, 272-2 are not limited in this respect and otherembodiments are within the scope of this disclosure. The first andsecond mounting surfaces 272-1, 272-1 extend in parallel relative toeach other but are offset by a distance D (see FIG. 7) to provide a stepstructure or profile. To this end, the arrangement of the first andsecond mounting surfaces 272-1, 272-2 may collectively provide a“stepped,” or multi-step mounting profile whereby the first and secondmounting surfaces are adjoined by a surface 299 that extendssubstantially transverse to each and provides the offset distance D. Theoffset distance D may measure between 10 and 130 microns, and preferably100 microns although other distances are within the scope of thisdisclosure.

The first mounting surface 272-1 may be substantially coplanar with thefirst mounting surface 245 of the substrate 202, or not, depending on adesired configuration. This may advantageously allow for electricaltraces 233 disposed/patterned on the first mounting surface 272-1 toelectrically couple with the substrate 202 via an interconnect devicesuch as the bus bars 235. Power and RF signals may be then provided tothe TOSA arrangement, and more particularly, optical components disposedwithin the cavity 260 of the housing 9. Accordingly, the first mountingsurface 272-1 may also be referred to as a feedthrough mounting surfaceas at least a conductive portion of the same, e.g., the conductivetraces patterned thereon, extends out from the cavity 260 of the housing209. The first mounting surface 272-1 includes a plurality of filteringcapacitors 231 mounted thereon. The filtering capacitors 231 may beutilized when driving the plurality of laser arrangements to maintainsignal integrity, e.g., by reducing noise, stabilizing the DC signal,for example.

On the other hand, the second mounting surface 272-2 is disposed withinthe cavity 260 of the housing 209 and is disposed at the offset D fromthat of the first mounting surface 272-1. The second mounting surface272-2 may be accurately referred to as an internal mounting surface or arecessed mounting surface whereby the mounting surface 272-2 is fullywithin the cavity 260 of the housing 209 and below the first mountingsurface 272-1. In addition, the second mounting surface 272-2 bevertically offset from the laser diode (LD) submounts 280-1, 280-2 suchthat the LD submounts 280-1, 280-2 are below a horizontal planeextending from the second mounting surface 272-2 (see FIG. 7). In otherembodiments, the second mounting surface 272-2 may be substantiallycoplanar with and proximate to the LD submounts 280-1, 280-2.

Continuing with FIG. 6, wire bonds 238 electrically couple the first andsecond LDD chips 242-1, 242-2 to laser diodes of the plurality of laserarrangements 274 and are relatively short to advantageously reduceissues such as time of flight (TOF) and impedance mismatches, forexample. Electrical interconnects other than wire bonds may be utilized,and the example embodiment of FIG. 6 should not be construed aslimiting.

The first and second LDD chips 242-1, 242-2 can electrically couple tothe plurality filtering capacitors 231 via wire bonds, for instance,although other types of interconnects are within the scope of thisdisclosure. In addition, the plurality of laser arrangements 274electrically couple to the electric traces 239 of the second mountingsurface 272-1. The electrical traces 239 then couple to the traces 233of the first mounting surface 272-1, and ultimately circuitry of thesubstrate 202, to complete an electrical circuit for RF and powersignals.

The cross-sectional view of FIG. 7 shows additional aspects of themulti-channel TOSA arrangement 204 in accordance with an embodiment. Asshown, the multiplexing device 225 and the plurality of laserarrangements 274 are supported by a thermoelectric cooler (TEC) 241. Tothis end, the TEC 241 can provide one or more mounting surfaces tocouple to active and/or passive optical components. The plurality oflaser arrangements 274 mount/couple to the TEC 241 via the LD submount,as shown, or can directly mount to the TEC 241 depending on a desiredconfiguration.

As further shown, first and second LD chips 242-1, 242-2 couple to andare supported by the second mounting surface 272-2. The first and secondLDD chips 242-1, 242-2 are therefore in thermal communication with thehousing 209 via feedthrough device 270 for heat dissipation purposes. Asshown in the embodiment of FIG. 7, an air gap 285 separates the firstand second LDD chips 242-1, 242-2 from the plurality of laserarrangements 274. Accordingly, the plurality of laser arrangements 274are in thermal communication with the housing 209 and/or the TEC 241 viaa first thermal conduction path 267 to dissipate heat. On the otherhand, the LDD chips 242 are in thermal communication with the housing209 via a second thermal conduction path 268 provided at least in partby the feedthrough device 270 that extends from the mounting surfaces272-1, 272-2 to the metal housing 209 to dissipate heat. The first andsecond thermal conduction paths 267, 268 are separate and distinct,which provides thermal isolation from each other as well as othercomponents of the multi-channel TOSA arrangement 204. Accordingly, lesspower may be consumed by the TEC 241 to ensure nominal performance ofthe multi-channel TOSA arrangement 204 based on the feedthrough device270 dissipating heat communicated from the first and second LDD chipsand/or filtering capacitors 231.

In operation, the multi-channel TOSA arrangement 204 receives an RFdriving signal and power from the substrate 202. In particular, theoptical components such as the plurality of laser arrangements 274receive the RF driving signal and power via the traces 233, 239. Inresponse, the plurality of laser arrangements 274 then modulate andlaunch channel wavelengths based on the received RF driving signal. Thechannel wavelengths are then received at the input region 282 of themultiplexing device 225. The multiplexing device 225 then multiplexesthe received channel wavelengths and outputs a multiplexed signal to thetransmit optical coupling receptacle 222 by way of output port 284 andintermediate fiber 294.

Feedthrough Architecture

As discussed above, one important consideration for multi-channel TOSAdesign is thermal performance to ensure heat gets dissipated duringoperation. Broadly speaking, thermal performance refers to a TOSA'scapability of operating within a particular range of operatingenvironment temperatures (e.g., ambient temperatures) while remaining ator below power consumption targets. Thermal performance considerationsinclude, among other things, ensuring that passive devices such asheat-communicating materials (e.g., heatsinks, submounts, and housings),and/or active temperature control devices (e.g., TECs) are chosen andarranged to accommodate a target number of channels and associatedcircuitry based on modeled/estimated power consumptions (e.g., inwatts).

In view of the foregoing, feedthrough devices consistent with thepresent disclosure include increased thermal conductivity to facilitateimproved thermal performance. The improved thermal conductivity allowsfor heat generating components mounted thereon, e.g., LDDs, tocommunicate heat in a manner that significantly reduces operatingtemperatures. The multi-channel TOSA arrangements discussed below withreference to FIGS. 8A-10B may be configured substantially similar tothat of the multi-channel TOSA arrangement 204 discussed above, thedescription of which is equally applicable to the embodiment of FIGS.8A-10B and will not be repeated for brevity.

For example, FIG. 8A shows an example cross-sectional view of amulti-channel TOSA arrangement 804, in accordance with an embodiment. Asshown in FIG. 8A the feedthrough device 870 includes a base portionformed of Alumina (Al₂O₃). Alumina provides a relatively rigid anddurable base, electrical isolation, but relatively poor thermalconductivity, e.g., about 12-35 W/m·K). This relatively no thermalperformance can be offset based on, for example, wires (e.g., formed ofGold or other heat-conductive material) that can transfer generated heatfrom LDDs to the cold-side of the TEC within the housing. However, evenwith this offset/mitigation provided by wire(s) and the TEC, the amountof power consumed to sufficiently cool the LDDs makes Aluminafeedthroughs impractical in various scenarios and applications.

FIG. 8B shows an isolated cross-sectional view of the feedthrough 870 ofFIG. 8A, in accordance with an embodiment. As shown, the feedthroughdevice 870 can include a base portion 872 and a plurality of additionallayers 874 disposed/formed thereon. The additional layers 874 can atleast partially define the first and/or second mounting surfaces 272-1,272-2, respectively, as discussed above. Alternatively, the base portion872 and plurality of additional layers 874 may also be provided as amonolithic structure formed from a single piece. In this embodiment, thethermal conductive path 268 includes a thermal conductivity of about12-35 W/m·K.

FIG. 9A shows another example cross-sectional view of a multi-channelTOSA module 904 in accordance with an embodiment. As shown, themulti-channel TOSA module 904 includes a feedthrough device 970 having acompound configuration formed by a plurality of different materiallayers. FIG. 9B shows that the compound configuration of the feedthroughdevice 970 can include a base portion 972 formed of copper tungsten(Cu—W) and at least one layer of Alumina 974 disposed thereon. Coppertungsten has a relatively high thermal conductivity of about 180 to 230W/m·K, and a relatively high electrical conductivity relative to othermaterials such as Alumina, e.g., a resistivity (μΩ·cm≤) of about 3.2 to6.5 depending on the composition.

The electrical and thermal properties of copper tungsten varies withdifferent proportions of tungsten and copper, and the provided examplesare not intended to be limiting. In any event, the compoundconfiguration advantageously utilizes the base portion 972 formed ofcopper tungsten to increase thermal communication with componentsmounted to the feedthrough device 870, and the at least one layer ofAlumina to electrically isolate the first and/or second mountingsurfaces 272-1, 272-2 from the metal forming base portion 972. Thepresent disclosure has identified that the compound configuration of thefeedthrough device 970 decreases operating temperatures of LDDs mountedto the feedthrough device 970 by 7-10 percent relative to the Aluminaconfiguration shown and discussed above in FIGS. 8A-8B.

FIG. 10A shows another example cross-sectional view of a multi-channelTOSA module 1004 in accordance with an embodiment. As show in FIG. 10B,the multi-channel TOSA module 1004 includes a feedthrough device 1070having a compound configuration formed by a plurality of differentmaterial layers. The base portion is collectively provided by a firstportion 1072 formed from Alumina and a second portion 1074 formed fromAluminum Nitride (AlN). The second portion 1074 defines at least aportion of the first and/or second mounting regions 272-1, 272-2 tocouple to and support components such as LDDs.

Aluminum Nitride has a thermal conductivity of about 285 W/(m·K), and insome instances up to 300 W/(m·K) depending on the composition. AluminumNitride also has a relatively high resistivity and can be used as anelectrical isolator. However, Aluminum Nitride is relatively fragilerelative to materials such as Alumina and Copper Tungsten. For example,Aluminum Nitride has a maximum tensile strength of about 197 MPa versusAlumina which has a maximum tensile strength of about 665 MPa.Accordingly, the embodiment of FIGS. 10A-10B includes a compoundconfiguration that combines the strength and rigidity of Alumina withthe thermal conductivity and electrical isolation of Aluminum Nitride.Notably, the first portion 1072 may be formed of tungsten carbide, orother suitable material, and this embodiment is not necessarily limitedto a specific material forming the base.

The present disclosure has identified that the compound configuration ofthe feedthrough device 1070 decreases operating temperatures of LDDsmounted to the feedthrough device 1070 by about 8-10 percent relative tothe Copper Tungsten configuration shown in FIGS. 9A-9B, and by about13-20 percent relative to the Alumina configuration shown in FIGS.8A-8B.

In accordance with an aspect of the present disclosure a transmitteroptical subassembly (TOSA) arrangement is disclosed. The TOSAarrangement comprising a housing having a plurality of sidewalls thatdefine a cavity therebetween, a feedthrough device having a first enddisposed in the cavity of the housing and a second end extending fromthe cavity away from the housing, the feedthrough device providing atleast a first mounting surface proximate the first end within thecavity, a first diode driver (LDD) chip mounted to the first mountingsurface of the feedthrough device, and a plurality of laser arrangementsdisposed in the cavity, each of the plurality of laser arrangementselectrically coupled to the feedthrough device to receive a radiofrequency (RF) driving signal from the LDD.

In accordance with another aspect of the present disclosure amulti-channel transceiver module is disclosed. The multi-channeltransceiver module comprising a substrate having at least a firstmounting surface for coupling to optical components, a multi-channeltransmitter optical subassembly (TOSA) arrangement electrically coupledto the substrate, the multi-channel TOSA arrangement comprising ahousing having a plurality of sidewalls that define ahermetically-sealed cavity, a feedthrough device having a first portionextending into the cavity and a second portion extending away from thecavity towards the substrate, a first laser diode driver (LDD) chipwithin the hermetically-sealed cavity and mounted to the first portionof the feedthrough device, a plurality of laser arrangements disposedwithin the cavity proximate the LDD chip, a plurality of electricalinterconnects electrically coupling each of the plurality of laserarrangements to the LDD chip, and a multiplexing device disposed withinthe cavity having an input region for receiving channel wavelengths fromthe plurality of laser arrangements and an output for launching amultiplexed optical signal having the received channel wavelengths on toa transmit optical fiber, a receiver optical subassembly (ROSA) coupledto the substrate.

In accordance with an aspect of the present disclosure a feedthroughdevice for use in optical subassembly arrangements is disclosed. Thefeedthrough device comprising a base portion formed of a layer of afirst material having a first thermal conductivity, at least one layerof a second material disposed on the base portion to provide at least afirst mounting surface for coupling to a heat generating component, thesecond material having a second thermal conductivity and providing athermal conduction path to communicate heat generated by the heatgenerating component, and wherein the first thermal conductivity of thefirst material is greater than the second thermal conductivity of thesecond material.

In accordance with another aspect of the present disclosure atransmitter optical subassembly (TOSA) arrangement is disclosed. TheTOSA arrangement comprising a housing having a plurality of sidewallsthat define a cavity therebetween, a feedthrough device having a firstend disposed in the cavity of the housing and a second end extendingfrom the cavity away from the housing, the feedthrough device providingat least a first mounting surface proximate the first end within thecavity, and wherein the feedthrough device comprises a base portion of afirst material and one or more layers of a second material disposed onthe base portion to provide the first mounting surface, and wherein thefirst and second materials have different respective thermalconductivities.

While the principles of the disclosure have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe disclosure. Other embodiments are contemplated within the scope ofthe present disclosure in addition to the exemplary embodiments shownand described herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentdisclosure, which is not to be limited except by the following claims.

What is claimed is:
 1. A feedthrough device for use in opticalsubassembly arrangements, the feedthrough device comprising: a baseportion to thermally couple to a mounting surface of an opticalsubassembly, the base portion having a first portion formed of a firstmaterial having a first thermal conductivity and a second portion formedof a second material having a second thermal conductivity, the firstportion abutting the second portion; at least a first mounting surfacedefined by the first portion of the base portion for coupling to a heatgenerating component; a thermal conduction path provided by the firstportion of the base portion extending from the first mounting surface ofthe first portion of the base portion to the mounting surface of theoptical subassembly without extending through the second material of thesecond portion to communicate heat generated by the heat generatingcomponent to the mounting surface of the optical subassembly; whereinthe first thermal conductivity of the first material is greater than thesecond thermal conductivity of the second material; and wherein thefirst material comprises Aluminum Nitride and the second materialcomprises Alumina.
 2. The feedthrough device of claim 1, wherein thefirst material has a first maximum tensile strength and the secondmaterial has a second maximum tensile strength, the first maximumtensile strength being less than the second maximum tensile strength. 3.The feedthrough device of claim 1, wherein the base portion defines asecond mounting surface for coupling to one or more electricalcomponents.
 4. The feedthrough device of claim 1, wherein the heatgenerating component comprises a laser diode driver (LDD).
 5. Atransmitter optical subassembly (TOSA) arrangement, the TOSA arrangementcomprising: a housing having a plurality of sidewalls that define acavity therebetween; a feedthrough device having a first end disposed inthe cavity of the housing and a second end extending from the cavityaway from the housing, the feedthrough device providing at least a firstmounting surface proximate the first end within the cavity; and whereinthe feedthrough device comprises a base portion having a first portionformed of a first material and a second portion formed of a secondmaterial, the first portion providing the first mounting surface, andwherein the first portion abuts the second portion and the first andsecond materials have different respective thermal conductivities;wherein the first material comprises Aluminum Nitride and the secondmaterial comprises Alumina; and wherein the first material of thefeedthrough device that comprises Aluminum Nitride provides a thermalconduction path extending from the first mounting surface to the housingwithout extending through the second material of the feedthrough devicethat comprises Alumina.
 6. The TOSA arrangement of claim 5, furthercomprising: a plurality of laser diode drivers (LDDs) mounted to thefirst mounting surface of the feedthrough device; and a plurality oflaser arrangements disposed in the cavity, each of the plurality oflaser arrangements electrically coupled to the feedthrough device toreceive a radio frequency (RF) driving signal from an associated LDD ofthe plurality of LDDs.